1. Field of the Invention
The present invention relates to a stainless steel separator for fuel cells and a method of manufacturing the same. More particularly, the present invention relates to a stainless steel separator for fuel cells and a method of manufacturing the same, which is used for polymer electrolyte fuel cells (PEMFCs) and exhibits superior corrosion resistance, electrical conductivity, and durability.
2. Description of the Related Art
Since a unit cell of a fuel cell stack generates too low a voltage to be used alone in practice, the fuel cell stack generally includes several to several hundred unit cells stacked therein. When stacking the unit cells, a separator or bipolar plate is used to facilitate electrical connection between the unit cells while separating a reaction gas.
The bipolar plate is an essential component of the fuel cell along with a membrane electrode assembly (MEA) and has a variety of functions, such as structural support for the MEA and gas diffusion layers (GDLs), collection and transfer of current, transmission and removal of reaction gas, transmission of water coolant for removing reaction heat, etc.
Hence, it is necessary for materials of the bipolar plate to have excellent electrical and thermal conductivity, air-tightness, chemical stability, and the like.
Graphite-based materials and composite graphite materials composed of resin and graphite are employed as the materials for the bipolar plate.
However, the graphite-based material has lower strength and air-tightness than metallic materials, and demands high manufacturing costs irrespective of low productivity when applied to the bipolar plate. Recently, metallic bipolar plates have been actively investigated to overcome such problems of the graphite bipolar plate.
When the bipolar plate is made of a metallic material, there are many merits in that volume and weight reduction of a fuel cell stack can be accomplished via thickness reduction of the bipolar plate, and in that the bipolar plate can be fabricated by stamping and the like, thereby ensuring mass production of the bipolar plates.
However, the metallic material inevitably undergoes corrosion during use of the fuel cell, causing contamination of the MEA and performance deterioration of the fuel cell stack. Further, a thick oxide film can be grown on the metal surface after extended use of the fuel cell, thereby causing an increase in internal resistance of the fuel cell.
Stainless steel, titanium alloys, aluminum alloys, nickel alloys, and the like are proposed as candidate materials for the bipolar plate of the fuel cell. Particularly, stainless steel has received attention due to its low price and good corrosion resistance, but further improvements in corrosion resistance and electrical conductivity are still needed.